When a communicating mobile station moves from one radio access network to another radio access network such that an access point is changed, continuity of a service may be damaged due to a handover operation. A change of an access point refers to a change of an administrative domain or a change of a subnet. Especially, handover between heterogeneous radio access networks entails a new authentication procedure. A delay generated by performing the authentication procedure retards termination of the handover procedure, and as a result affects a currently served multimedia session.
Meanwhile, in the institute of electrical and electronics engineers (IEEE) 802.21 standard, handover between heterogeneous networks is actively being discussed. A range of the IEEE 802.21 standard for media independent handover (MIH) is to provide intelligence to a link layer and to establish a standard for transmitting related network information for optimal handover to a higher layer. This includes wired and wireless networks of IEEE 802-series (referred also to as “802-series” for simplicity), as well as a link specified by the 3rd generation partnership project (3GPP)/3GPP2. Namely, the IEEE 802.21 standard has a purpose of improving user convenience by supporting handover between heterogeneous networks (referred also to as “Inter-RAT handover” for simplicity) and supports cooperative use of available information in a mobile terminal and a network. To this end, an access point of a network, such as a mobile terminal or a base station, should provide multi-mode operation, which means that multiple radio standards are supported and simultaneous connection over one or more radio interfaces is allowed.
An MIH function defined by the IEEE 802.21 standard serves to determine handover as a logical entity. The MIH function is located in both a mobile terminal and a network and enables the mobile station and the network to exchange information about setting or status of an access network in the vicinity of the mobile terminal. The MIH function may be referred to as “MIH entity” in order to discriminate between other entities performing other functions.
FIG. 1 illustrates a protocol layer configuration of a mobile terminal, an 802-series network, and a 3GPP/3GPP2 network.
A multi-mode mobile node 101 may include interfaces according to communication modes. FIG. 1 shows the mobile node 101 including a 3GPP/3GPP2 interface 104 and an 802-series interface 105. Such interfaces are divided into a physical (PHY) layer and a medium access control (MAC) layer. In FIG. 1, an 802-series network 102 and a 3GPP/3GPP2 network 103 include interfaces 106 and 107, respectively.
Meanwhile, MIH layers represented as MIH functions 108, 109, and 110 are located under a higher layer including an Internet protocol (IP) layer. The MIH layers define not only handover between 802-series interfaces but also handover between an IEEE 802-series interface and an interface defined by the 3GPP/3GPP2. Namely, the MIH function easily executes a handover process between heterogeneous networks by acquiring information about other networks from a layer 2 (for example, a MAC layer).
FIG. 1 illustrates higher layer functions 111, 112, and 113 of the mobile node 101, the 802-series network 102, and the 3GPP/3GPP2 network 103. The higher layer functions 111, 112, and 113 may be referred to as MIH users or MIH user entities in terms of MIH.
FIG. 2 illustrates a handover procedure between heterogeneous radio access networks by an MIH-based multi-mode mobile terminal.
In FIG. 2, a multi-mode mobile terminal 201 of a current access network performs handover to a network Y of a target network while being served by a network X 202. It is assumed in the mobile terminal 201 that a MAC1 201c and a MAC2 201d are entities which perform layer-2 communication with the network X 202 and the network Y 203, respectively.
The multi-mode mobile terminal 201 which is communicating while maintaining connection with the network X 202 acquires information about a neighbor network (for example, the network Y 203) from the network X 202 (step S201). In this case, information related to layer-2 security, such as an authentication method and an encryption algorithm, can be acquired through an information service defined in the MIH function. The mobile terminal 201 receives signals from the neighbor network through scanning and carries out a network detection and selection procedure (step S202).
Meanwhile, if a signal level received from the serving network X 202 is lower than a prescribed level, the interface MAC1 201c reports this to an MIH 201b of a higher layer through a local event trigger and to an MIH 202b of the network X 202 through a remote event trigger (step S203). The MIH 202b of the network X 202 requests an MIH 203b of the network Y 203 to be handed over to transmit IP information (step S204). The network Y 203 receiving the IP information request transmits the IP information to the mobile terminal 201 through the network X 202 (step S205). The mobile terminal 201 receiving the IP information of the network Y 203 can previously acquire an IP address which is to be used during handover to a corresponding network.
For handover to the network Y 203, the MIH 201b of the mobile terminal 201 commands that a MAC (i.e., MAC2 201d) of a corresponding interface perform a procedure for layer-2 handover (step S206). Then the mobile terminal 201 performs the layer-2 handover procedure to the network Y 203 by implementing a network initial registration procedure including the authentication and security related procedure (steps S207 and S208).
If the mobile terminal 201 completes the layer-2 handover (network registration procedure) with the network Y 203, the MAC2 201d of the mobile terminal 201 reports this to a higher layer 201a for layer-3 handover (step S209). The mobile terminal 201 performs the layer-3 handover including a procedure for registering care-of-address (CoA) acquired from a new network (network Y 203) to a home agent. If the handover is completed, the mobile terminal 201 initiates communication with a new network (step S210). Next, the mobile terminal 201 disconnects an old network (network X 202) (step S211).
As described above, Inter-RAT handover of a multi-mode mobile terminal defined in the IEEE 802.21 newly performs an authentication and encryption key acquisition procedure while the mobile terminal performs layer-2 handover to a new network. Accordingly, substantial delay of a user service is expected and data may be damaged.